For prevention of the chemotherapy-induced stomatitis we administered allopurinol mouthwash to 15 out of 38 patients who underwent PMUE regimen. The severity of stomatitis was graded on five scales according to the criteria of Japan Society For Cancer Therapy. The incidence of stomatitis was defined as patients number with stomatitis above Grade 2/all patients number. Six of 23 patients which were not given allopurinol mouthwash (control group) developed stomatitis of Grade 1 (three patients), Grade 3 (two), or Grade 4 (one). Only one patient given allopurinol mouthwash (AMW group), however, suffered from Grade 1 stomatitis. The incidence of stomatitis was 13.0% for a control group and 0% for an AMW group. The average graded toxicity was 0.07 for the AMW group significantly lower than 0.57 for the control group. There was no significant difference between the two groups in other clinical adverse effects or abnormal laboratory data. These results suggested that allopurinol mouthwash regimen was well tolerated and effective for prevention of the chemotherapy induced stomatitis.